Process for producing blended cements with reduced carbon dioxide emissions

ABSTRACT

A process for producing blended cement, where the cement contains Portland Cement mixed thoroughly with a microfiller and possibly a water reducing agent to a dry cement mixture and fine supplementary cementitious materials selected from the materials blast furnace slag, fly ash, quartz, silica, amorphous silicon dioxide, limestone and recycled concrete.  
     The invention is characterized in, that said supplementary materials in a first step are being subjected to a grinding in a dry state to a specific surface of at least 1000 cm 2 /g (Blaine), in that in a second step the supplementary grinded materials are being subjected to a grinding together with at is least 20% by weight of the total grinding mass of a highly reactive cement mixture in a dry state to achieve a specific surface of at least 3000 cm 2 /g (Blaine), which highly reactive cement mixture contains cement and at least one of the components a SiO 2  containing microfiller and a polymer in the form of a powdery water-reducing agent which mixture have been previously been treated in a grinder with vibrating grinding media in which the cement particles are subjected to a large number of impact impulses giving the cement particles an increase in surface energy and chemical reactivity.

[0001] The present invention related to process of producing hydraulicblended cement with a significantly reduced Portland clinker mineralscontent and correspondingly with an increased amount of supplementarymaterials.

BACKGROUND

[0002] It is well known that each ton of production of Standard PortlandCement is accompanied by the release of about one ton of carbon dioxideand that about half of this comes from the decarbonisation of limestonein the kiln and the other half from energy consumption, primarily in thekiln.

[0003] It follows that the only way in which the cement industry canachieve meaningful reductions in carbon dioxide emissions is via thereduction if Portland clinker production and increased use of fillers.The cement industry does not believe that more than about 2-3% furtherreduction in energy consumption is possible in Standard Portland Cementproduction.

[0004] The traditional methods of production of blended cement includeintergrinding Portland cement clinker with different types ofmicrofillers, e.g. blast furnace slag, fly ash, limestone etc. mainly inrotating ball mills. Such methods are not providing more than 20-25% ofPortland clinker replacement by fly ash and approximately 30-50% byblast furnace slag, without significant negative influence on the cementperformance, such as decrease of setting time, very low strengthdevelopment during the curing period 0-28 days, etc. It takes up to 3times longer time (2-3 months) to achieve a 28-days strength oftraditionally Portland Cement concretes. At the same time the highvolume fly ash (HVFA) cements do have significant benefits in comparisonwith traditional Portland cements. Concretes produced with such cementsare characterized by high durability, such as a low chloridepermeability, a high sulphate and an alkali-silica resistance, etc., seee.g. Malhotra, Concrete International J., Vol 21, No. 5, May 1999, pp.61-66. According to Malhotra strength development of such concretescould be improved by significantly increasing the content of a binder,such as cement+a microfiller and significantly decreasing the amount ofmixed water, but such approach require increased dosages of waterreduced admixtures to keep acceptable consistency of concrete mixtures,which sharply increases the cost of the concrete.

[0005] Another method related to the present invention is a methoddescribed by the US Patent Appln. Publ. No. US 2002/0000179 for a“Method for producing a blended cementitious composition”. Saidapplication suggests to introduce into the concrete mixtures of PortlandCement and traditional cementitious materials as fly ash, blast furnaceslag, etc. very fine and highly reactive rice hull ash. This gives animprovement of early age strength and chloride permeability of theconcretes.

[0006] Such method of producing concrete requires increased amounts, upto 400 kg per cubic meter, of a binder material, such as cement+flyash+rice hull ash, in order to achieve a concrete which is comparable toStandard Portland Cement concretes at relative low water-to-binderratios, such as less than 0.40. Those requirements bring significanttechnical and economical limitations for the application of said methodby the ready mix concrete industry which produces about 95% of theconcrete with a cement/binder content of 250-300 kg per cubic meter anda water to cement ratio of 0.60-0.70. Introduction of said method forthe mentioned concrete mix design leads to a drastical decrease of theconcrete strength development and increase of the setting time, whichmake it non-competitive with Standard Portland Cement concretes.

DISCLOSURE OF THE INVENTION

[0007] The present invention refers to the process for producingenvironmentally efficient blended cements with reduced carbon dioxideemissions for the preparation of concrete, where said cements containPortland Cement mixed thoroughly with a microfiller and probably a waterreducing agent to obtain a highly-active and dry cement mixture.

[0008] The present invention refers to a process for producing blendedcement, where the cement contains Portland Cement mixed thoroughly witha microfiller and possibly a water reducing agent to a dry cementmixture and fine supplementary cementitious materials selected from thematerials blast furnace slag, fly ash, quartz, silica, amorphous silicondioxide, limestone anal recycled concrete and is characterized in, thatsaid supplementary materials in a first step are being subjected to agrinding in a dry state to a specific surface of at least 1000 cm²/g(Blaine), in that in a second step the supplementary grinded materialsare being subjected to a grinding together with at least 20% by weightof the total grinding mass of a highly reactive cement mixture in a drystate to achieve a specific surface of at least 3000 cm²/g (Blaine)which highly reactive cement mixture contains cement and at least one ofthe components a SiO₂ containing microfiller and a polymer in the formof a powdery water-reducing agent which mixture have been previouslybeen treated in a grinder with vibrating grinding media in which thecement particles are subjected to a large number of impact impulsesgiving the cement particles an increase in surface energy and chemicalreactivity.

[0009] The said supplementary materials are subjected to a separatepreliminary grinding to achieve a specific surface at least 1000 cm²/g(Blaine) and then to the joint grinding with at least about 20 weightpercent, of the total grinding mass, of a highly reactive cement mixtureto achieve a specific surface at least 3000 cm²/g (Blaine). This resultsin an improvement of hydraulic reactivity in the case blast furnace slagis used. The improvement of chemical reactivity with calcium hydroxideis achieved in the case of the use of silica or other substancescontaining silicon dioxide. The improvement is due to the surfacemodification of the particles of the said blend in the form ofmicrodefects, microcracks and dislocations caused by strained induceddynamic transformations caused by the grinding process.

[0010] According to a very advantageous embodiment of the presentinvention, said highly reactive cement mixture has been manufacturedaccording to a method according to the European Patent No. 0 696 262.

[0011] It is however also possible to use a cement mixture that has beentreated in accordance with a corresponding process so as to obtain acompressive strength corresponding to that recited in EP 0 696 262.

[0012] European Patent Specification No. EP 0 696 262 describes a methodof producing cement that can be used to producing cement that can beused to produce pastes, mortar, concrete and other cement-basedmaterials of high bearing capacity with reduced water content, highmechanical strength and density and rapid strength development. Thismethod includes the mechanical-chemical treatment of a mixture of cementand at least one component of two components, wherewith the firstcomponent is a microfill that contains silicon dioxide and the secondcomponent is a polymer in the form of water reducing agent. The cementand the first and/or the second component are mixed in the first stagein a dry state, wherewith the particles in the first and/or the secondcomponent are adsorbed on the cement particles. The mixture obtained inthe first stage is treated in the second stage in a grinder withvibrating grinding media in which the particles in said mixture aresubjected to a large number of impact impulses which change directionsin a rapid sequence and therewith result in modification of the surfaceproperties of cement particles in the form of considerable increase insurface energy and chemical reactivity. The duration of treatment in thesecond stage is sufficient for a cement paste cube having tie sidelength of 20 mm and compacted thoroughly under vibration and cured at+20 degrees C. under sealed conditions to obtain a one-day compressivestrength equal to at least 60 MPa.

[0013] The European Patent No. 0 696 262 is hereby incorporated in thepresent patent application.

[0014] The present invention also relates to a method for producing aconcrete mixture.

[0015] The method is used for preparing shaped concrete elements orstructures and comprises the steps of firstly producing a blended cementaccording to the above said method and secondly mixing the said blendedcement with sand and/or aggregate of greater dimensions and water, andthirdly casting a shaped element or the structure and hardening of thesubject.

[0016] The present invention will be described more in detail in thefollowing partly in connection with Tables and Figures, where

[0017]FIG. 1 is a diagram showing the average case for the particle sizedistribution of the blended cements produced according to the presentinvitation in comparison with traditionally Portland Cements and initialblend subjected to grinding according to proposed methods. It shows thatthe specific surface of the said blended cements is in line with thespecific surface of tile commercially produced pure Portland Cements.

[0018] Table 1 and 2 respectively shows the strength development of theEN mortar, which is a European standard, having a cement-to-sand ratioof 1:3 and a water-to-binder ratio of 0.50, and concretes with aleblended cements containing high volume of fly ash produced according tothe present invention and traditional blended cements.

[0019] Table 3 represents the strength development of the EN mortar(cement-to-sand ratio 1:3, and water-to-binder ratio 0.50) and concretewith blended cements containing a high volume of quartz filler producedaccording to the present invention.

[0020] Table 4 represents the strength development of the EN mortar(cement-to-sand ratio 1:3, and water-to-binder ratio 0.50) with blendedcements containing a high volume of blast furnace slag producedaccording to the present invention and traditional blended cement.

[0021] In tables 4 and 5 HRC stands for High Reactive Cement as forexample cement treated according to EP 0 696 262.

[0022] Table 5 represents the test results from the testing of chloridepermeability (ASTM C 1202-94) of the concretes with blended cementscontaining a high volume of quartz filler produced according to thepresent invention.

[0023] It has been discovered that when supplementary cementitiousmaterials selected front the group of materials, e.g. blast furnaceslag, fly ash, quartz, silica or other substance containing amorphoussilicon dioxide, etc., firstly subjected to a separate preliminarygrinding to achieve a specific surface at least 1000 cm²/g (Blaine), andsecondly subjected to joint grinding with at least about 20 weightpercent of highly-reactive cement mixture to achieve a specific surfaceat least 3000 cm²/g (Blaine) the finally obtained blended cement hassignificantly better performance than traditional blended cements. Thebetter performance relates to a higher early-age and long-term strengthdevelopment, a finer porosity, etc. It has also a better performancethan pure Portland Cement, such as a significantly higher environmentalprofile, a higher long-term strength development, a significantly lowerchloride permeability, etc.

[0024] The above mentioned above grinding, both the separate and thejoint stages, could be realized with the use of media milling equipment,e.g. tumbling ball mills, vibratory ball mills, planetary mills, stirredand centrifugal mills, and a non-media milling equipment e.g. roller,jet mills, etc.

[0025] According to one preferred embodiment of the present inventionthe blended cement contains from 20% by weight up to 80% by weight ofsaid highly reactive cement mixture.

[0026] According to a first embodiment said supplementary cementitiousmaterial substantially consists of Class F fly ash.

[0027] According to a second embodiment said supplementary cementitiousmaterial substantially consists of Class C fly ash.

[0028] According to a third embodiment said supplementary cementitiousmaterial substantially consists of granulated blast furnace slag.

[0029] According to a fourth embodiment said supplementary cementitiousmaterial substantially consists of a quartz filler with a silicondioxide content of at least 80% by weight

[0030] According to ASTM C 618 fly ash classified in two classes, ClassC and Class F. Class F fly ash typically contains more than 70% byweight of silica, alumina, and ferric oxides, while Class C typicallycontains between 70% and 50% Class F produced as a by product of thecombustion of bituminous coal Class C fly ash has a higher calciumcontent and produced as a by product of thi: combustion ofsub-bituminous coal

EXAMPLES

[0031] The following materials have been used in these experiments:Standard Portland cement CEM I 42.5 according to EN-197 or Type Iaccording to ASTM C 150, fly ash Class (FA), blast furnace slag (BFS),and quartz filler (Q). Chemical compositions of the said materials arepresented by Table 6.

[0032] The cementitious supplementary materials have been subjected toseparate grinding in the vibrating mill VBM 1518 to achieve a specificsurface approximately 1500 cm²/g (Blaine).

[0033] Then the said fillers have been mixed in a dry state with ahighly reactive dry cement mixture produced according to European PatentSpecification No. EP 0696262 and containing 99% of PC and 2% of fly ashClass F. The mixing of the said components have been performed with amixer called “Tonimix”, manufactured in Germany, with a rotation speedof 280 rpm during 3 min. to obtain a homogeneous blend.

[0034] The said blends have been subjected to further grinding in arotating ball mill to achieve the specific surface of about 4500 cm²/g(Blaine).

[0035] During these two subsequent grindings the particles ofcementitious supplementary materials are subjected to a surfacemodification in the form of microdefects, microcracks and dislocationscaused by strained induced dynamic transformations. Such effects lead tothe improvement of hydraulic reactivity in the case blast furnace slagis used and improvement of chemical reactivity with calcium hydroxide inthe case of that silica or other substances containing silicon dioxideare used.

[0036] According to the test results the blended cements producedaccording to the proposed invention have specific surfaces in line withStandard Portland Cements, see FIG. 1, and the properties related tostrength development and durability are significantly better than fortraditional blended cements and pure Portland Cements, see tables 2-5.

[0037]FIG. 1. shows the particle size distribution for the blendedcements produced according to the proposed grinding method and particlesize distributions for the blends before grinding Please see thenotations in the FIG. 1.

[0038] Due to a significant reduction of Portland clinker contentimplementation of such blended cements could significantly reduce thelevel of carbon dioxide and other “green house” gases emissions, wherethe reduction could be more than 50%, and the amount of energy requiredfor Portland clinker production. TABLE 6 Chemical composition CompoundPC FA BFS Q CaO 62.4% 15.0% 35.5% 0.1% SiO₂ 17.8% 49.4% 34.0% 98.2%Al₂O₃ 4.0% 19.6% 11.5% 0.2% Fe₂O₃ 3.9% 5.2% 0.4% 0.3% SO₃ 3.2% 0.8% 3.4%0.1% Na₂O <0.1% 0.3% 0.54% 0.3% K₂O 0.3% 1.2% 0.56% 0.2%

[0039] TABLE 1 Tests with fly ash for EN mortar (blended cement producedaccording to the proposed invention. Compressive strength, MPa for flyash, % weight Type of mi 0 30 40 50 EN-mortar 18.6 23.8 18.6 14.4EN-mortar 42.7 52.9 46.8 43.7 Concrete*, 14.0 13.8 13.5 13.0 Concrete*,33.8 43.7 36.1 35.0

[0040] TABLE 2 Test with fly ash for EN mortar (traditionally blendedcements). Curing time, days Cement type 2 7 28 80% PC + 20% fly ash .523.6 35.8 60% PC + 40% LFA 0.8 17.7 29.6

[0041] TABLE 3 Tests with quartz filler for EN mortar Compressivestrength, MPa for quartz filler, % by cement weight Type of mixture 0 3040 50 EN-mortar, 2 days 18.6 20.4 17.6 15.4 EN-mortar, 28 days 42.7 44.943.8 42..7 Concrete*, 2 days 14.0 13.8 13.5 13.0 Concrete*, 28 days 33.836.7 36.1 35.0

[0042] TABLE 4 Tests with blast furnace slag for EN mortar SlagCompressive strength, MPa content, for curing time, days Type of mixture% 2 7 28 100% PC  0 18.1 36.9 47.7 60% PC with slag 40 16.1 30.2 48.2(traditional blend) 60% HRC with slag 40 19.5 38.4 55.6 30% HRC withslag 70 10.0 36.8 52.7 20% HRC with slag 80 8.0 30.2 49.9

[0043] TABLE 5 Results from the testing of chloride permeability (ASTM C1202-94) Average value of “Charge passed” and Evaluation of Mix Binderw/b- (SD) chloride No type) ratio (Coulombs) permeability 1 100% PC 0.453734 (165) Moderate 2 100% PC 0.50 4030 (135) High 3 100% PC 0.60 4828(448) High 4 50% HRC + 0.45 763 (62) Very Low 50% quartz filler 5 50%HRC + 0.50 821 (39) Very Low 50% quartz filler 6 50% HRC + 0.60 976(106) Very Low 50% quartz filler

[0044]FIG. 1

[0045] Notations:

[0046] Q stands for reference blend of Standard Portland Cement andquarts filler (<1 mm), ratio 50/50 by weight.

[0047] EQ stands for the blend of Standard Portland Cement and quartzfiller (50/50) unterground according to EMC method.

[0048] FA stands for reference blend of Standard Portland Cement and flyash Class F ratio 50/50 by weight.

[0049] EFA stands for blend of Standard Portland Cement and fly ashClass F ratio 50/50 by weight unterground according to EMC method.

[0050] ST7 stands for Standard Portland Cement (Type I according to ASTMC 150).

[0051] IN4 stands for Rapid Hardening Portland Cement (Type IIIaccording to ASTM C 150 with higher fineness).

[0052] Calculated surfaces in m²/liter in brackets behind legends.

1. A process for producing blended cement, where the cement contains Portland Cement mixed thoroughly with a microfiller and possibly a water reducing agent to a dry cement mixture and fine supplementary cementitious materials selected from the materials blast furnace slag, fly ash, quartz, silica, amorphous silicon dioxide, limestone and recycled concrete characterized in, that said supplementary materials in a first step are being subjected to a grinding in a dry state to a specific surface of at least 1000 cm²/g (Blaine), in that in a second step the supplementary grinded materials are being subjected to a grinding together with at least 20% by weight of the total grinding mass of a highly reactive cement mixture in a dry state to achieve a specific surface of at least 3000 cm²/g (Blaine), which highly reactive cement mixture contains cement and at least one of the components a SiO₂ containing microfiller and a polymer in the form of a powdery water-reducing agent which mixture have been previously been treated in a grinder with vibrating grinding media in which the cement particles are subjected to a large number of impact impulses giving the cement particles an increase in surface energy and chemical reactivity.
 2. Process according to claim 1, characterized in, that said highly reactive cement mixture has been manufactured according to the method according to the European Patent No. 0 696
 262. 3. Process according to claim 1 or 2, characterized in, that the blended cement contains from 20% by weight up to 80% by weight of said highly reactive cement mixture.
 4. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of Class F fly ash.
 5. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of Class C fly ash.
 6. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of granulated blast furnace slag.
 7. Process according to claim 1, 2 or 3, characterized in, that said supplementary cementitious material substantially consists of a quartz filler with a silicon dioxide content of at least 80% by weight.
 8. Method for producing a concrete mixture, characterized in, that it comprises firstly the steps of claims 1 to 7 to produce said blended cement and secondly the step of mixing said blended cement with sand and/or aggregates of greater dimensions and water and possibly a water reducing agent and an air entraining additive. 